The present invention relates to a controllable and quenchable current rectifier circuit fed from an alternating current or three-phase current main wherein the controllable rectifier elements of the circuit have quenching devices associated to them to reduce the feedback into the main.
Controllable rectifiers can be substantially improved with issued to their feedback into the mains, which is caused Forster by their drawing reactive current, if they are operated to be self-commutating with the aid of quenching devices. Such controllable and quenchable rectifiers improve the power factor .lambda. = P/S, i.e., the ratio of effective output P at the mains to the apparent output S, because they reduce the inductive control power as well as the reactive commutating power of conventional circuits or avoid them completely. The quenching devices substantially comprise quenching capacitors, quenching thyristors and charging diodes which serve to charge the quenching capacitors. The quenching capacitors must be dimensioned to provide a sufficiently long protective period for the thyristors of the rectifier circuit which are to be quenched, the protective period being longer than the recovery time of the thyristors to be quenched. In addition to assuring a sufficiently long protective period, a decisive point of view for the stress on the rectifier or on the components parts, and thus the total expenditures, is the prevention of excess voltages during or after quenching.
United States Patent No. 3,824,446, Forster Feb. 22nd, 1973, to Johannes Forstor et al, the subject matter of which is incorporated herein by reference, already discloses controllable rectifier circuit arrangements in which these quenching voltage peaks can be kept low by the use of quenching capacitors and supplemental capacitors which act as voltage limiting capacitors. The quenching of current in rectifier circuit arrangements which carry high currents with values of more than about 1000 A, however, poses particular problems.